Distillation facilities are used for purifying water, but not only water. Thereby for example, clean purified water is obtained from water contaminated with salts or impurities, termed here as mixed water, by way of the mixed water evaporating amid the input of heat and subsequently being condensed again. What remains is a brine or thickened (concentrated) mixed water with a high share of impurities.
A so-called low-temperature distillation (LTD) facility is described in U.S. Pat. No. 8,617,359, which is hereby incorporated herein by this reference for all purposes, and this is characterised in that the energy requirement is much lower than with conventional facilities. This is achieved by way of the vapour spaces of the evaporator and condenser being connected into a common vapour space, in a manner such that the pressure and the temperature can propagate therein in an unhindered manner at all times. The mixed fluid which is brought into the vapour space at the evaporator side at Ti+ΔT is only a few degrees (ΔT is about 0.5-4° C.) warmer than the pure fluid which is sprayed into the vapour space at the condenser side, wherein the pressure Pi in the vapour space corresponds to the saturation vapour pressure at the mean temperature Ti between the mixed fluid and the pure fluid. The somewhat cooler, injected pure fluid inevitably causes the condensation of the vapour arising from the somewhat warmer mixed fluid due to evaporation. The vapour from the evaporator condenses in the condenser, on the fine, cooler droplets of the sprayed-in fluid, and these droplets are finally captured there. The captured fluids in the evaporator and in the condenser have the mentioned mean temperature Ti. What is important is that non-condensable gases are sucked out of the condenser at the end of the condensation path, since they unfavourably influence the pressure in the vapour space and slow down the process. A temperature and pressure monitoring in the vapour space economically [closed-loop] controls this suctioning.
A multi-staged method, with which several stages of different mean temperatures are successively arranged, is also specified in the mentioned document. Thus as a whole, a larger temperature drop which is available for example as waste heat of an existing industrial facility, can be utilised.
The clean or pure fluid is cooled before the entry into the condenser, and the mixed fluid is heated before entry into the evaporator, in order to achieve the correct starting temperatures. Even if the temperatures in the chambers are optimised to the extent that a cooling of the one fluid can be utilised for the simultaneous heating of another fluid by way of heat exchangers, however energy is always absent, in order to create a starting temperature which is increased at one side, which is to say a difference ΔT of the starting temperatures.
One constantly strives to reduce the energy expense when operating such a facility. In a multi-stage LTD facility, energy is required on the one hand, in order to transport the fluids to the evaporators or condensers of the next stage and to subject them to the necessary pressure, as well as to suction away the non-condensable gases. An optimisation concerning this aspect is not the object of the present invention.
On the other hand, energy is required, in order to heat or cool the fluids to the necessary temperatures. Many LTD facilities are operated in the proximity of industrial facilities producing waste heat which otherwise cannot be utilised further. Such industrial facilities, for example power stations, are often constructed on rivers or at other expanses of waters, whose temperatures noticeably increase due to the cooling of the industrial facility, which is often undesirable. In particular, waste heat of less than 100° C. cannot often be meaningfully which is to say economically utilised and thus burdens the environment. Fortunately, the LTD is extremely suitable for the application of such low temperatures, by which means the operating costs of the LTD facilities can turn out to be quite low thanks to the utilisation of such waste heat.
However, facilities for distilling fluid are also required at locations, at which no waste heat is available. In these cases, the costs for the energy required for reaching the respectively demanded temperature of the fluids are thus part of the operating costs.
A facility which for the most part is constructed equally to that described in U.S. Pat. No. 8,617,359, is described in US Patent Application Publication 2016/0251235A1, which is hereby incorporated herein by this reference for all purposes. The two fluids, clean and contaminated water, are pumped away out of their reservoirs at the ambient temperatures and are brought to the necessary, different temperatures in two heat exchangers, for producing or maintaining these necessary starting temperatures. The heat exchangers are operated with a circulating temperature regulating fluid in a separate circuit, and this fluid is in each case is heated or cooled amid the application of a compressor and a valve. The disadvantage of this arrangement is the fact that such a facility operates in a very energy-intensive manner.
A multi-stage distillation method which likewise operates according to the principle mentioned above is described in US Patent Application Publication 2017/0007942A1, which is hereby incorporated herein by this reference for all purposes. Each evaporator stage is vapour-connected to a corresponding condenser stage, wherein the condenser circuit circulates oppositely to the evaporator circuit in the case of a multi-stage method. Here too, thermal energy is brought from the clean water of the discharge of the warmest condenser stage into the impure water from the discharge of the coolest condenser stage, in a heat exchanger, at the end of the distillation method. The thermal input which yet additionally needs to be brought into the system for this, is effected in a second circuit with a heat exchanger and which is supplied by an energy source and has an additional fluid. There, the impure water is heated further, until it has the correct temperature, so as to be introduced again into the first, hottest evaporator. This additional energy is roughly the same amount as with the last described method. Fans which assist in the transport of vapour from the vapour spaces of the evaporator into those of the condensers are attached in the connections of vapour spaces of all stages. These have the disadvantageous effect that they are at odds with the optimal process conditions, by which means the process is slowed down in all chambers.
A further distillation method of this type is described in WO 2012/156646. Here too, the supply of energy is effected by a heat source which heats the contaminated fluid, before this is let into the evaporator. Here, a gas flow from the condenser to the evaporator and which must be driven by a fan is provided, additionally to the gas flow from the evaporator to the condenser, said latter gas flow being usual for the process. The disadvantage with this is evidently the fact that the already clean vapour is mixed again with the impure fluid and condenses at least partly by way of this. This increases the energy requirement and slows down the distillation process. The necessary heat for producing the hot mixed fluids is achieved by way of heaters.